1. Field of the Invention
The present invention relates to an apparatus for efficiently and stably producing oxygen-enriched air from atmospheric air and, particularly, to an oxygen enriching apparatus suitable for medical purposes.
2. Description of the Related Art
In the treatment of patients suffering from respiratory ailments such as asthma, emphysema, and chronic bronchitis, one of the most effective therapies is oxygen inhalation. In this regard, an oxygen enriching apparatus which can be operated at the patient's bedside to extract oxygen from the atmosphere and to produce oxygen-enriched air has attracted attention as a simple source of oxygen for oxygen inhalation purposes. Oxygen enriching apparatuses for such purposes are classified generally into two types: an adsorption separation type employing an adsorbent, such as zeolite, which adsorbs nitrogen selectively at a higher rate than oxygen, and a membrane separation type employing selectively permeable membranes which permit the permeation of oxygen at a higher rate than nitrogen.
Both the adsorption separation type and the membrane separation type of oxygen enriching apparatus utilize a motor-drive pump. In the adsorption separation type, the atmosphere is compressed by the pump to 1 to 3 kg/cm.sup.2 G, and the compressed atmosphere then brought into contact with an adsorbent to adsorb nitrogen. In the membrane separation type, the pump is used to maintain the oxygen-enriched air, which has permeated through the selectively permeable membranes, at a vacuum of 100 to 300 torr to provide oxygen-enriched air having a preselected oxygen concentration.
Because these apparatuses utilize different types of pumps, the noise level of the membrane PG,4 separation type oxygen enriching apparatus is lower than that of the adsorption separation type oxygen enriching apparatus, and hence the former is more suitable for home use. However, the conventional oxygen enriching apparatus is not satisfactory from the viewpoint of noise suppression, in that the noise level thereof is still too high. Particularly, a low-noise oxygen enriching apparatus which will not disturb the patient's sleep during the night has not yet been provided.
Several measures to reduce noise are well-known, such as sealing off the noise source with sound insulating walls, damping the vibration of the noise source to suppress sound propagation through solid forms, and attenuating the sound by applying a sound absorbing material to the inner surface of walls enclosing the sound source.
Such noise suppressing measures are applied to the conventional oxygen enriching apparatus, but their effect is unsatisfactory. For instance, when a sound insulating wall for sealing off the noise source is used, the mass of the sound insulating wall is increased to enhance the sound insulating ability thereof. However, an excessive increase in the wall thickness of the sound insulating wall causes an undesirable increase in the weight and size of the apparatus. Conversely, when the noise propagated through the air inlet and air outlet is greater than the noise transmitted through the walls, the limitation of the general noise level of the apparatus is dependent on the noise propagated through the air passage, and hence the sound insulation of the walls is ineffective.
The application of an insulating material to the inner surface of the air passage is sometimes unsatisfactory, in that if an excessive thickness must be applied, the cross sectional area of the air passage is excessively reduced, which increases the air flow resistance of the air passage thus reducing the flow rate of the air, which sometimes causes problems such as insufficient cooling of the pump and other components. Thus the prior art has been unable to provide satisfactory measures to suppress the noise of an oxygen enriching apparatus without causing a deterioration in the performance of the oxygen enriching apparatus and increasing the weight and size of the same.
Moreover, most conventional membrane separation type oxygen enriching apparatuses operate with a fixed number of membrane elements. Such an oxygen enriching apparatus is capable of providing oxygen-enriched air having a preselected oxygen concentration when the temperature of the ambient air is approximately normal. However, in hot seasons such as summer, where the ambient temperature exceeds, for example, 30.degree. C., such an oxygen enriching apparatus is able only to provide oxygen-enriched air of an oxygen concentration far lower than the preselected oxygen concentration. Furthermore, in the conventional oxygen enriching apparatus operating under a high ambient temperature, the flow rate of the oxygen-enriched air is excessively high, and hence the surplus oxygen-enriched air is unavoidably discharged into the atmosphere to no purpose.
In the prior art, an oxygen enriching apparatus equipped with a control valve for each oxygen-permeable membrane element has been proposed in order to vary the number of operational oxygen-permeable membrane elements. Such an oxygen enriching apparatus, however, requires sophisticated and expensive control valves and complicated operating procedures. Further, in conventional membrane separation type oxygen enriching apparatus, the condensate obtained by cooling the oxygen-enriched air is discharged from a moisture separator through a drain pipe packed with filaments. Sometimes, the condensate contains foreign matter, such as solid substances produced in the drain pipe by NOx and SOx dissolved in the condensate and particles produced by the diaphragm vacuum pump. This foreign matter is liable to accumulate in the vicinity of and clog the inlet of the drain pipe, impeding the normal draining of the condensate.
Also, during discharge of the condensate, the condensate is liable to spatter from the outlet of the drain pipe onto components lying around the outlet of the drain pipe, to corrode the components or to leak outside the apparatus.
In a medical oxygen enriching apparatus, in particular, it is important to drain the condensate stably under all conditions for an extended period of operation throughout all seasons so that an appropriately humidified oxygen-enriched air not containing water droplets is supplied to the patient. Supplying oxygen-enriched air in which moisture is insufficiently removed, i.e., containing water droplets, is unhealthy, and the spattering from the drain is unsanitary. Accordingly, such an oxygen enriching apparatus is not at all suitable for medical purposes, and thus there is a strong demand that such problems of the conventional oxygen enriching apparatus be solved as soon as possible.
Since medical oxygen enriching apparatuses, in particular, are used at the patient's bedside in the hospital or in the home, sanitary oxygen-enriched air having a preselected oxygen concentration must be supplied by those apparatuses. However, in the conventional oxygen enriching apparatus, occasionally the motor for driving the pump cannot be started when the operation of the apparatus is restarted immediately after an interruption of the operation, which is disadvantageous from the viewpoint of accessibility. It is important that the oxygen enriching apparatus be accessible and stable in operation.